Added docs and C bindings for AccessibleStateSet and AccessibleRelationSet.

Added docs and C bindings for AccessibleStateSet and AccessibleRelationSet.
Improved listener API docs and listed legal signals (other than GTK+ signals,
which are documented in GTK+ itself).
C bindings documentation coverage is now 100%.
Changed Registry.idl slightly, added two methods to DeviceEventController API.
Some work towards non-preemptive key listeners.
Fixed regression in signal connection caused by changes to Gtk+.
Connected bridge to all signals, so they should be available if they are emitted.

git-svn-id: http://svn.gnome.org/svn/at-spi/trunk@96 e2bd861d-eb25-0410-b326-f6ed22b6b98c